The present invention is directed toward improving the resistance of hearing device sound ports to contamination. More specifically, the invention is directed toward improving the resistance of “completely in the canal” (CIC) hearing devices to ear wax (i.e. cerumen, which is produced in the ear) and water which can impinge on the sound ports from a shower, a pool, or perspiration from outside or within the ear.
The vast majority of hearing assistance devices are air conduction hearing aids, meaning that sound enters the device via the air and is transmitted from the device to the tympanic membrane of the patient via air. Sound waves traveling in the air impinge on a microphone which generates an electrical signal that is processed, amplified, and drives a speaker (called the “receiver” in the hearing aid art) which sends amplified and processed sound waves in air toward the tympanic membrane of the patient. Thus, most hearing aids have a sound port for the microphone and a sound port for the receiver. If these sound ports get plugged or otherwise compromised by contaminants, the hearing aid's performance degrades.
The nature of contaminants that can affect sound ports depend on the location of the sound ports, which in turn depends on the type of hearing aid. For example, the microphone port in a conventional BTE (Behind The Ear) device is located on the module suspended on the pinna, and is susceptible to water and debris from the environment and hair, but is not susceptible to wax. In contrast, the receiver port of a conventional CIC (completely in the canal) hearing aid is susceptible to cerumen and moisture produced in the cartilaginous portion of the ear canal where the receiver port is typically located. It is desirable to have sound ports that are resistant to contamination and do not distort the acoustic signals as the sound waves pass through the ports. Hearing aid designers and manufacturers have attempted many approaches, but none of the approaches attempted to date meets the requirements of extended wear CIC hearing aids which are worn deep in the canal for extended periods of weeks or months.
Extended wear hearing devices, such as those described in U.S. Pat. No. 7,215,789 to Shennib et al., U.S. Pat. No. 6,940,988 to Shennib et al., and U.S. Pat. No. 6,473,513 to Shennib et al., are worn continuously for periods from several weeks to several months inside the ear canal. These devices as taught by Shennib et al. are miniature in size in order to fit entirely within the ear canal and are adapted for the receiver to fit deeply in the ear canal in proximity to the tympanic membrane (TM). However, the devices' microphone port, as taught, is exposed to the cartilaginous portion of the canal, and consequently the cerumen, moisture, and debris that could be present.
In U.S. Pat. No. 6,738,488, Baker teaches a hearing aid with features to protect the receiver sound port. Features include a tortuous path that allows sound to reach the eardrum, but impede the flow of cerumen to the receiver. Additional features include a shield, and a mesh, also to stop cerumen Inherent in the design is the need to remove the device and clean the mesh and shield in the event it gets clogged by cerumen, which Baker acknowledges is likely. With regard to protection from water, the teaching is less convincing because it requires a particular orientation of the hearing device with respect to gravity, and during an average wearer's day, the head can be in may orientations with respect to gravity. Furthermore, the local forces of capillary action, fluid adhesion, and fluid cohesion are not discussed, and in fact dominate the effect of gravity. The designs of the Baker's patent would not pass a high fidelity signal into a microphone, nor would they protect a device that remains in the ear for extended periods from wax and water.
In U.S. Pat. No. 4,984,277, Bisgaard et al teach a protection element for an all-in-the-ear hearing aid. The protection element is properly designed acoustically, but contains a wax filter which is replaced. Replacement of the filter requires the removal of the device from the ear and special tooling. The approach of Bisgaard and similar filter methods are therefore not appropriate for a device that is intended to remain in the ear for extended periods without cleaning the device.
In U.S. Pat. No. 4,972,488, Weiss and Stanton teach protection schemes based on tortuous paths similar to those of Baker. The teachings acknowledge that such tortuous paths will have an impact on the acoustic transfer function. Most significantly, in the Weiss patent as well as the Bisgaard and Baker patents, emphasis is placed only on wax protection. Water and moisture are not considered, and in fact water would flood and wick into the protection schemes without additional precautions due to capillary action in the tortuous paths.
In order to design sound ports resistant to the relatively hostile environment of the ear canal, all of water, soapy water, perspiration, cerumen and debris need to be considered.